Phenylalanine sensing based on surface plasmon resonance.

A phenylalanine sensing system was constructed with photochromic spiroxazine derivative via surface plasmon resonance (SPR). Recognition-functional spiroxazine monolayer was formed on Au surface by self-assembly. After spectroscopic characterizations of monolayer, various concentrations of d- and l-phenylalanine were employed as analytes on UV addressable ring-opened spiroxazine monolayer. The different SPR angle shift derived from interaction between d- and l-phenylalanine and spiroxazine monolayer can be explained by the different dipole moment of ionic complexes. Computer simulations using Molecular Orbital PACkage AM1 approximation reinforced the reliability of the experimental results. To confirm the long-time stability of spiroxazine monolayer, we measured SPR response of spiroxazine monolayer with repetitive UV-on and off. These experimental results suggest that it can be applicable to simple analysis of interaction between zwitterionic recognition-functional molecule and analyte.